This invention relates to an electric servo system which is unaffected by the change of or the variation in a load acting as an object to be controlled, the external disturbance, and the effect of friction at a sliding portion.
The electric servo system is utilized for a drive unit of a computer peripheral apparatus such as a magnetic tape and a magnetic disc, of a terminal apparatus such as an optical character reader, a facsimile and a laser beam printer, and of a robot. The quantity to be controlled in the electric servo system includes displacement, speed and the like.
In the electric servo system of this type of closed loop system, a very important consideration is to ensure that its transfer characteristic should be unaffected by the exchange of or the variation in the load, the external disturbance and the effect of friction at the sliding portion. A prior art as disclosed in an article entitled "Basic Study on Design of Low-sensitivity and High-speed Electric Servo" announced in Jan. 31, 1981 recognizes this importance. The elimination of load influence upon the transfer characteristic intended by the present invention is likewise discussed in this article but it is different from the present invention in the resolving manner.
In spite of the study in this field of technology, the elimination of the influence of the exchange of or variation in the load, external disturbance and effect of friction at the sliding portion upon the transfer characteristic of an electric servo system is still insufficient and practically, various machines and apparatus with the electric servo system cannot be controlled stably and accurately. For example, where the load is increased in its moment of inertia under the condition that the transfer characteristics of electric servo system is set to be an optimum for a small moment of inertia of the load, it happens that displacement or speed of the load becomes oscillatory. Also, under an effect of external disturbance upon the electric servo system, displacement or speed of the load varies. For these reasons, the controllable quantities cannot follow up target values with high-fidelity in the conventional electric servo system.